java - 使用 isALive() 或连接方法时出错

Question

我正在尝试使用 isALive 和 join 方法，但它抛出一个错误，如找不到符号....请告诉我这个程序中的错误到底在哪里。join 方法的用途是什么。我知道这是等待线程完成，但我想要详细信息。

class newthread1 implements Runnable {
    newthread1() {
        Thread t = new Thread(this, "FirstThread");
        System.out.println("Child Thread:" + t);
        t.start();
    }

    public void run() {
        System.out.println("We are in processing for 1st thread");
        int p = 1000, t = 3;
        double r = 3.5, si;
        try {
            si = (p * r * t) / 100;
            System.out.println("Simple Interest:" + si);
        } catch (ArithmeticException e) {
            System.out.println("Error:" + e);
        }
    }
}

class newthread2 implements Runnable {

    newthread2() {
        Thread t = new Thread(this, "SecondThread");
        System.out.println("Child Thread:" + t);
        t.start();
    }

    public void run() {
        try {
            System.out.println("We are in processing for 2nd thread");
            double a, r = 4.3;
            int p = 1000, n = 3;
            double temp = Math.pow((1 + r / 100), n);
            a = temp * p;
            System.out.println("Compound interest:" + a);
        } catch (ArithmeticException e) {
            System.out.println("Error:" + e);
        }
    }
}

class mainthread {
    public static void main(String args[]) {
        newthread1 t11 = new newthread1();
        new newthread2();
        boolean b = t1.t.isAlive();
        System.out.println("Thread is alive:" + b);
        t1.t.join();
    }
}   

Answer 1

解决方案 1
将您的主要方法更改为

class mainthread {
    public static void main(final String args[]) throws InterruptedException {
        Thread thread = new Thread(new newthread1());
        newthread1 t11 = new newthread1();
        new newthread2();
        boolean b = thread.isAlive();
        System.out.println("Thread is alive:" + b);
        thread.join();
    }
}

并运行线程调用thread.start()，创建可运行对象的实例不会自动开始运行。您明确告诉线程开始或停止。

解决方案 2
或者您可以将 Thread 对象 '' 创建为 global variable 并将类更改为

class newthread1 implements Runnable {
    public Thread t;

    newthread1() {
        t = new Thread(this, "FirstThread");
        System.out.println("Child Thread:" + t);
        t.start();
    }

    @Override
    public void run() {
        System.out.println("We are in processing for 1st thread");
        int p = 1000, t = 3;
        double r = 3.5, si;
        try {
            si = p * r * t / 100;
            System.out.println("Simple Interest:" + si);
        } catch (ArithmeticException e) {
            System.out.println("Error:" + e);
        }
    }

    public Thread getT() {
        return t;
    }
}

然后是main方法

class mainthread {
    public static void main(final String args[]) throws InterruptedException {
        newthread1 t11 = new newthread1();
        new newthread2();
        boolean b = t11.t.isAlive();
        System.out.println("Thread is alive:" + b);
        t11.t.join();
    }
}